The Local Interconnect Network (LIN) bus standard is an open protocol defined for use in communicating between a number of distributed modules. Such communication standards may typically refer to systems in which a plurality of similar modules are used on a common bus line, and in which each module may need to be addressed individually. A LIN bus system may comprise a master node that is connected via a wired connection, e.g. by a single data wire forming a common signal conductor, to at least one slave node. Thus, the master node and slave node(s), connected by the data wire, form a network cluster. These slave devices may form control components associated with identical and/or different functions to be controlled by the master device. For example, such functions that can be controlled by a LIN data bus system, as known in the art for automotive applications, are window lifting, seat heating, motor control or power generation.
Particularly, the LIN bus is a serial bus that is often, but not exclusively, used in automotive applications. For example, such an application may be a low-end, e.g. relatively cheap and easy to implement, sensor network in a vehicle, e.g. a network connecting multiple sensors and/or actuators to a master node in a vehicle. Each module in the cluster may have a unique identity, represented by an ID code, which may be programmed as a unique identifier in the node or assigned to the node by an auto-addressing method, as known in the art. This unique identity enables the master node to communicate with a selected slave node or a selected group of slave nodes.
The LIN bus provides a communication architecture for bidirectional exchange of data between the master node, on one hand, and each slave node, on the other hand. Each module may contain an interface circuit, which may be implemented as a single integrated circuit for providing the functionality of the module, and in which this interface circuit is adapted for interfacing with the common signal conductor and for implementing the protocols associated with the messages and responses exchanged via the LIN bus.
However, in a LIN bus system as known in the art, the maximum number of nodes associated with a single bus may be restricted to 16 nodes, e.g. due to the protocol definitions pertaining to the physical layer and/or due to the capacitive load on the network. For example, the LIN physical layer specification, revision 2.0, clearly states that the number of nodes in a cluster should not exceed 16, in order to prevent that the network impedance could prohibit fault-free communication under worst case conditions, for example due to a presumed lowering of about 3% of network resistance by each additional node.
Nonetheless, particular applications may require cluster sizes that comprise a larger number of modules. For example, in an automotive application such as control signal communication for interior ambient lighting, a cluster size in the range of twenty to fifty nodes may be commonly required. Furthermore, the number of nodes to be preferably included in a cluster may go up to two hundred nodes, or even higher, for particular applications.
It is known in the art to control a plurality of devices, e.g. lights, by a single electronic control module, which may be slave node in a bus network. However, such direct control, as known in art, may require a dedicated control wire for each controlled device connecting to the control module, and may thus have a disadvantageous cost, system complexity, resistive losses and/or interference risk associated therewith due to the wires and connectors required.
For example, as shown in FIG. 1, in an automotive interior lighting system, as known in the art, each LIN slave node 102 may control a three-coloured light emitting diode light (LED) 101, e.g. a red-green-blue colour triplet LED (RGB-LED). Thus, each LIN slave node 102 may receive information associated with a selected colour and brightness from a central electronic control unit (ECU) 103 acting as a master node, via the LIN Bus, and may be adapted for returning diagnostic information to the master node.
Therefore, it is desirable to implement a larger number of nodes in a single LIN bus cluster, e.g. more than 16 nodes per cluster. Approaches known in the art to connect more than 16 nodes in a single network may have various disadvantages, such as a high system cost for a central electronic control unit (ECU) that is specifically adapted for acting simultaneously as a master node 103 on a plurality of separate LIN buses 104, as shown in FIG. 1, in which each of these LIN subnetworks 104 conforms to a maximum of 15 slave nodes.
A high cost of such system may be, at least partially, associated with the additional requirements for supporting multiple input and output (I/O) ports, higher memory requirements and more advanced and/or faster processing capabilities to determine the correct interface connection for routing a particular message and for handling inbound and outbound traffic on multiple busses simultaneously. For example, the central ECU 103 may be required to calculate and manage all information for all connected light sources, to coordinate the control of each and every connected light. This may generate a high protocol load, e.g. dense message traffic, as each slave node 102 will receive its light control information from the central ECU and may also transmit diagnostic information towards the central ECU in return.
Furthermore, due to the large number of wired connections of the ECU that are required to control multiple LIN buses, electromagnetic compatibility (EMC) issues may arise due to electric field coupling, e.g. capacitive coupling, between the wires. While such EMC issues could be resolved by including additional decoupling capacitors, this would also disadvantageously increase the system. The EMC issues may need to be solved by additional capacitors thereby increasing the total system cost. Moreover, the space requirements for the wire harness, particularly in the direct vicinity of the central ECU, may be high, such that other design parameters may be disadvantageously affected, e.g. introducing constraints in mechanical design.